semester 1 exammm Flashcards
what is atomic radius
distance from outermost electron to nucleus
atomic radius decreases left to right across a period due to:
atom’s increasing nuclear charge &
high nuclear charge increases attraction of electrons, bringing them closer to the nucleus therefore decreasing atomic radius
what is ionisation energy
amount of energy needed to remove an electron from a neutral atom in the gaseous state
e.g. metals like lithium have low ionisation energy
non metals have high ionisation energy as they almost have a full valence shell
ionisation energy increases from left to right across a period
what are the 3 factors that explain the trends of the periodic table
- atom’s nuclear charge: great nuclear charge the more strongly electrons are attracted to the nucleus
- atomic radius: as the distance between the nucleus and outermost electron increases, the strength of electron attraction decreases
- sheilding by inner shell electrons: electrons in the inner shell repel other electrons between the nucleus and the outer electrons, blocking some of the atom’s electronegativity to the outer electrons
what is effective nuclear charge
number of protons in nucleus - number of inner shell electrons
increases left to right: as nucleus becomes more positive attraction between nucleus and electrons becomes stronger (increasing effective nuclear charge.)
more energy needed
decreases down group: electrons get further from nucleus and are less strongly bound - sheilding effect is greater
what is successive ionisation energy
energy needed to remove subsequent electrons
values become larger because electrons are being removed from ions which have increasing positive charges
explain electronegativity
definition: the electron attracting power of an atom in a molecule
metals have low electronegativity values
non metals have high electronegativity values
increases across a period:
decreases down a group:
what is emission spectra
when atoms absorb energy e.g. heat they become exited & can move up to a higher energy level (an e- shell thats further away)
when the e- moves back into its original position it releases light energy in all different directions
the light will have a specific wavelength unique to each element
for each particular element, all atom energy levels are identical
what are the 3 different types of spectra
emission spectroscopy
atomic absorption spectroscopy (AAS)
mass spectrometry
explain what atomic absorption spectroscopy (AAS) is
used to perform quantitative analysis (find amount of element present)
relies on electron transfer between atomic energy levels
uses the absorption of light by the atoms electrons to measure how much of an element is present
the lamp used for this process is made out of the same element being tested
e.g. if you were testing for zinc, you would use a zinc lamp
the light emitted has a unique set of wavelengths unique to the element.
what is the best analytical technique for determining the isotopic concentration of a sample
atomic absorption spectroscopy
explain the process of an atomic absorption spectrometer
- an electric current is passed through a gaseous sample of the element so it will emit light
- the light emitted has a unique set of wavelengths
- the sample is vaporised
- the light from the lamp is passed through the vaporised sample
- the element being tested for will absorb the light
- light enters the monochromator which focuses on 1 wavelength by the detector
- detector measures amount of light passed through the sample that is not absorbed
what is an isotope
atoms that have the same atomic number but different mass number (number of protons)
share the same chemical properties (due to same number of valence electrons)
physical properties (mass) will differ
what is relative atomic mass
actual atomic mass is too small to calculate
it is the mass of the atom compared to 1 twelfth of the mass of a carbon-12 atom
its an average of all naturally occurring isotopes present
list the properties of metal
good conductors of heat and electricity in solid & liquid state
shiny surface
hard
malleable
ductile
insoluble in water
reasonably high MP
very high BP
describe metallic bonding
particles arranged as a lattice of positive cations surrounded by a sea of delocalised electrons
delocalised: can move around atoms and through the lattice
explain the metallic property of heat/electricity conduction
when heated energy of cations and delocalised electrons increases
this energy is conducted along metals as cations and electrons collide, transferring electricity
when metals conduct electricity, electrons from one end of the metal cause a similar number of e- to be displaced from the other end
in sold: only electrons move
liquid: both cation and e- carry charge
explain the metallic property of malleability and ductility
bonding in metals is NON DIRECTIONAL
layers of atoms can slide over each other without destroying metallic bond
explain the metallic property of MP & BP
MP and BP indicate strength of intermolecular forces
relatively high MP and BP due to strong attraction between positive cations and mobile electrons
explain the metallic property of hardness
strength of bond is related to charge of positive cations in lattice
metals in group 2 are stronger because atoms release 2 valence electrons (instead of 1 in group 1) and form ions with a +2 charge
list the ionic properties
non conductors of electricity in solid state
good electrical conductors in molten or liquid state
hard
brittle
relatively high MP
relatively high BP
varying solubilities in water, insoluble in non-polar solvents
describe ionic bonding
ionic solid:
positive and negative ion are arranged in an orderly 3D lattice
each positive ion is surrounded by negative ions and vice versa
ions are held in fixed positions by strong ionic bonds
Explain the ionic property of conducting heat/electricity
solid: non conductors because ions are held in a fixed lattice, no mobile charged particles
molten: ions are now mobile, both positive and negative ions carry charge
aqueous: ions dissociate and are able to carry charge
Explain the ionic property of MP and BP
high MP and BP:
ionic bonding has large electrostatic forces of attraction between holding atoms together in a lattice
large amount of energy is required to overcome strong ionic bonds
Explain the ionic property of hardness
strong ionic bonding extends throughout lattice solid
scratching requires overcoming strong ionic bonds
Explain the ionic property of brittleness
ionic lattice doesn’t withstand distortion
when lattice is distorted, like charges align and repel, shattering lattice
Describe covalent molecular substances
exist only as discrete molecules
non metals only
solid, liquid or gaseous state
intramolecular forces: strong covalent bond hold atoms together within a molecule
intermolecular forces: weak forces of attraction between molecules
list the properties of CMS
non conductors of electricity in solid and liquid
some are weak/good conductors in aqueous solutions
malleable
soft
low Mp and BP
mostly insoluble in water, soluble in non-polar compounds
examples: F2, H2O, O2
explain the covalent molecular property of electricity conduction
non conductors in aq, s or l:
molecules are uncharged
electrons are held tightly within covalent bonds
**exception: some CMS react with water to form ions, and become conductors in aqueous solutions
explain the covalent molecular property of softness
weak intermolecular forces require little effort to overcome: easy to separate molecules
strong covalent bonds aren’t disrupted
explain the covalent molecular property of malleability
molecules can easily slide or be pushed
only weak intermolecular forced exist between them, these can easily be reformed
explain the covalent molecular property of BP and MP
low BP and MP:
when CMS are heated, little energy is needed to overcome weak intermolecular forces
Describe covalent network substances
solid state only
non metals only
carbon with different structures are called allotropes:
diamond and graphite
examples of CNS substances: silicon, silicon dioxide, carbon
List the properties of covalent network substances
non conductors of heat and electricity in solid and liquid state **exception: graphite
extremely brittle
extremely hard
high MP and BP
insoluble in water and most other solvents
reasonably chemically inert
Describe the bonding of covalent network substances
arranges in an infinite lattice structure
explain the CNS property of electricity/heat conduction
non conductors: no mobile electrons because all valence electrons are tied up in covalent bonds **exception: graphite
explain the CNS property of brittleness
if some bonds are broken, the rest of the lattice is placed under stress and shatters
explain the CNS property of hardness
extremely hard:
breaking strong covalent bonds requires a very large amount of energy
explain the CNS property of MP and BP
high MP and BP:
each atom is held in place by strong covalent bonds
breaking these bonds requires a very large amount of energy
explain the CNS property of solubility
insoluble in water & most other solvents:
vary large amount of energy is required to re-arrange existing bonds in any dissolving process
explain the CNS property of chemical inertness
reasonably chemically inert:
all bonding requirement are fulfilled
very large amounts of energy required to re-arrange existing bonds
Briefly describe the structure and property of diamond
structure:
each carbon atoms is attached to 4 other atoms in a 3D arrangement called a tetrahedron
properties: high MP (>3550˚C) non conductor of electricity brittle extremely hard
Briefly describe the structure and property of graphite
structure:
each carbon atoms is covalently bonded to 3 other atoms to form flat 2D sheets called graphene
one valence electrons from each carbon remain delocalised
properties:
high MP
good conductor of electricity
soft
what does the mole represent in mole/mass calculations
measure of the number of particles in a substance
1 mole of any substance contains 6.022 x 10(23) particles
what does molar mass represent in mole/mass calculations
equal to atomic, molecule and formula masses in grams
What is mass spectrometry used for
determines mass and relative abundance of each isotope present in a sample of an element
describe the process of mass spectrometry
involved 4 steps: vaporisation ionisation acceleration detection
- sample is vaporised
- electrons are fired at the sample and are used to knock off electrons from the atoms, forming ions
- ions are accelerated and are deflected through a magnetic field (heavier ions are deflected less than lighter ions)
- Ions are detected and produces a mass spectrum
list 3 separation techniques
sieving
filtration
evaporation
Briefly describe the separation technique of filtration
liquid passes through filter paper (filtrate) ad solid residue is left behind
used for:
separating very fine solid particles from liquids and gases
Briefly describe the separation technique of sieving
mixture is passed through a sieve, a series of sieves may be used
based on different sizes of components, smaller particles will pass through the hole, larger particles will get caught
used for:
separating solids from liquids
e.g. straining pasta
what are the classifications of matter
pure substances: contain 1 type of particle
- elements: contain 1 type of atom e.g. Ca, O2
- compounds: contain 2 or more different types of atoms
e. g. H2O, NaCl
mixtures: contain 2 or more different types of particles
- homogenous
- uniform composition
- e.g. air, soft drinks
- heterogenous
- non uniform composition
- e.g. dirty water, paints
what determines the shape of molecules
the arrangement of electrons pairs surrounding the central atom
what does VSEPR stand for and what does this theory state
stands for valence shell electron pair repulsion
theory states that electrons pairs in the valence shell of an atom repel each other, and are arranges as far apart as possible
what does polarity refer to
related to the sharing of the bonding electrons between atoms
what is the difference between a polar and non polar bond
non polar: electrons are shared evenly between atoms, equal charge distribution
polar: electrons are not shared evenly between atoms because different atoms have different electronegativities
explain what a polar bond is
occurs between atoms with 2 different electronegativities
electrons spend more time moving around the atom with the greatest electronegativity
this leads to an uneven charge distribution in the bond
the region near the more electronegative atoms has a partial negative bond
the region near the less electronegative atoms has a partial positive bond
this is called a bond dipole
what is an extreme polar bond
occurs between non metal atoms with large differences in electronegativities e.g. F and H
what are intermolecular forces
weak attractive forces existing between molecules
list the different types of intermolecular forces
dispersion: attraction between all types of particles resulting in instantaneous dipoles
dipole-dipole: attraction between polar molecules
hydrogen bonds: attraction between polar molecules containing OH, NH or FH groups
ion-dipole: attraction between polar solvent water molecules and dissolved ions
explain what dispersion forces are
temporary dipoles form between molecules in order for them to change shape
temporary polarity: electrons are constantly moving around atoms and are not always symmetrically distributed across the atom
this temporary asymmetrical distribution produces a temporary/instantaneous dipole
if it is close to another molecule w/ a temporary dipole, it will cause polarity in the neighbouring atom
these two temporary dipoles will be attracted to one another
this force between molecules is dispersion force
how can you predict the strength of dispersion forces
increase in strength with increasing number of electrons
- as ayomic radius increases, e’ have greater space to
mover and greater chance to arrange asymmetrically
molecular shape
the larger the surface area over which the electrons can develop an instantaneous dipole and the closer molecules can fit next to each other, the strogner the dispersion force
explain what dipole-dipole forces are
weak attractive forces between polar molecules
molecule that has a partial negative charge is attracted to neighbouring molecule with partial positive charge
the more polar the molecules, the stronger the force will be
explain what hydrogen bonding is
dipole-dipole forces containing NH, OH or FH as they’re the most electronegative atoms
very polar bond –> stronger dipole dipole forces
more energy required to overcome bonds: higher BP
atomic radii are smaller - high charge density at the end of each molecule
e- are attracted more strongly toward N, O or F
what are the requirements for hydrogen bonding
presence in 1 molecules of at least 1 NH OH or FH covalent bond
presence of another polar molecule containing at least 1 N, O or F atoms with a non-bonding pair of electrons
define hydrogen bond
the attractive force between the lone pair of electrons on the N, O of F atom on on of the polar molecules and the partially positive charge of the H bonded to N, O of F on the second polar molecule
what are the unique properties of water
relatively high MP (O˚) and BP (100˚)
density of water in the solid phase is lower than its density in liquid phase
high surface tension
explain water’s property of its density
water has a maximum density of 1.0g ML-1 as a liquid at 4˚
when freezed it expands significantly and density drops by 8%
reduced density is why ice floats on water and freezes top down providing a layer of insulation preventing the rest of the water from freezing
this is because of the crystal lattice formed when water freezed - each water molecule can form 4 hydrogen bonds, maximising hydrogen bonding but takes up more space
explain water’s property of its high surface tension
water has strong intermolecular forces
imbalance of these forces at waters surface causing water molecules to be pulled inward toward the bulk of the liquid
as a result the surface tries to contract to minimise surface area
what is chromatography
separates compounds in a solution with the same properties
paper chromatography: separates a mixture of solutes with difference solubilities of absorption
explain the process of chromatography
uses paper and a solvent that can move over the medium
samples are placed along chromatography paper and paper is dipped in a solvent and left to dry
solvent will run up the paper, dissolving the samples
different solubilities cause some samples to run further up the paper than others
liquid with the lowers BP is first to evaporate and be distilled out of the paper and collected
what are the physical properties of intermolecular forces
changing phase
solubility
equilibrium vapour pressure
explain the physical property of changing phase for intermolecular forces
MP and BP of substances increases as intermolecular force strength increases
as molecular mass increases (number of e’), MP and BP increases
substances that have dipole-dipole forces have a slightly higher MP and BP
substances that have hydrogen bonding have a slightly higher MP and BP
explain the physical property of solubility for intermolecular forces
a solute and solvent can only form a solution if the attractive forces between molecules are comparable in strength
e,g, non polar molecules (dispersion forces) can’t be soluble in polar substances (dipole-dipole)
